2.0 Analysis 2.1 Flight Path A reconstruction of the aircraft's flight path shows that a descending 30-degree banked turn with an average acceleration of 1.2 g would be required to follow the calculated flight path. Since this flight path was well within the performance capabilities of the aircraft and is consistent with the aircraft wreckage, it is the most likely accident scenario. The aircraft was observed in normal flight shortly before the accident, no defects were found with the aircraft's engine and flight controls, and the weather was not a factor. It is likely, therefore, that the pilot lost situational awareness and allowed the aircraft to descend to the ground as a result of some degree of incapacitation. 2.2 Medical Factors The symptoms experienced by the pilot on 26 June 1994, three days before the accident, are consistent with those of an inner ear disorder. The pilot may have suffered from this disorder without other indications of illness, because the disorder can be present without other outward indications. Because recovery from the disorder may take from four to six weeks, the vertigo that occurred on 26 June may have recurred at the time of the accident, although this cannot be proven. If a period of vertigo similar to the one of 26 June occurred in flight, the pilot could have become incapacitated as a result. Although tests did not reveal the presence of agricultural chemicals or solvents, their presence cannot be ruled out because agricultural chemical solvents are volatile. If such solvents were present, they may have adversely affected the pilot's performance. The pilot's precautions against contact or ingestion of the agricultural chemicals being used were consistent with those observed by other pilots in the industry. However, the pilot's precautions were not as extensive as those recommended by the chemical manufacturers. 2.3 Fatigue The pilot's flying schedule shows that, although he began the 1994 application season in late April, the busiest part of the season started in June. Because agricultural application requires low winds to limit drifting of the spray, most flights took place early in the morning or in the evening. In addition to his flying duties, the pilot had the responsibility of operating his business. The time spent planning and carrying out business-related duties increased the pilot's workload and reduced the amount of time available during the day for sleep. Although the pilot did not exceed the 30-day maximum flying time, he sometimes exceeded the 15-hour daily on duty time. Because the pilot sometimes napped during the day, he experienced a disturbance in his sleep patterns. Though it cannot be proven, it is possible that fatigue contributed to the pilot's loss of situational awareness. 2.4 Survival Aspects The impact with the ground was not survivable because of the high deceleration forces. In an impact at lower speed, however, the failure of the pilot's shoulder harness would have been a factor affecting the chances of survival. The harness is checked at regular maintenance intervals by visual inspection, but, because the harness stitching between fabric layers is not visible, a visual inspection of the harness at maintenance intervals would probably not reveal any weakening of such stitching. 3.0 Conclusions 3.1 Findings The pilot was certified and qualified for the flight in accordance with existing regulations. The aircraft's technical records indicate that, except for the control cables, the aircraft was certified and maintained in accordance with existing regulations. The engine was producing power at the time of impact with the ground. No evidence of a failure or malfunction in any of the aircraft's systems was found. The aircraft struck the ground in a descending turn at a speed in the normal cruise speed range. The pilot experienced symptoms of dizziness and vertigo three days before the accident. The cause of these symptoms could not be determined; however, they were most likely the result of an inner ear disorder. The pilot's flying and non-flying duties resulted in long hours of work. As a result, he may have been suffering from fatigue. Toxicological testing did not reveal the presence of agricultural chemicals or solvents; however, because of the volatility of the solvents, their presence cannot be ruled out. 3.2 Causes The exact cause of the accident could not be determined. While en route to his destination, the pilot most likely became incapacitated to such a degree that he allowed the aircraft to enter a descending turn and strike the ground. The pilot's incapacitation may have been caused by an inner ear disorder. Possible contributing factors were fatigue resulting from the pilot's work schedule, and the effects of agricultural chemicals. The Board has no aviation safety recommendations to issue at this time.4.0 Safety Action The Board has no aviation safety recommendations to issue at this time.